The present invention relates to an improvement in a liquid crystal projector.
In a conventional liquid crystal projector, a transmission type liquid crystal display panel displays an image, and the image on the panel is projected and enlarged on a screen surface. The conventional liquid crystal projector has the following arrangement.
FIG. 1 shows a typical conventional liquid crystal projector. Reference numeral 1 in FIG. 1 denotes a transmission type dot-matrix liquid crystal display panel; and 2, a light source arranged behind panel 1. Light source 2 comprises lamp 3 and parabolic reflector 4 for reflecting light from lamp 3 in a direction parallel to optical axis O. Light source 2 thus emits illumination light A parallel to axis O toward panel 1. Reflector 4 in light source 2 in the liquid crystal projector comprises a parabolic reflector in FIG. 1. However, in a conventional liquid crystal projector using a conventional elliptical reflector as the light source reflector, a relay lens is arranged in the light source, and the light from the lamp is corrected by the relay lens to obtain collimated light. The collimated light is then incident on the liquid crystal display panel. Reference numeral 5 denotes a projection lens arranged in front of panel 1. The light passing through panel 1, i.e., an image displayed on panel 1 is enlarged by lens 5, and an enlarged image is projected onto screen S. Panel 1 is of a TN (Twisted Nematic) type. Panel 1 is inclined at a predetermined angle with respect to optical axis O such that illumination light A from the rear side of the panel has the highest efficiency. Reference numeral 7 denotes a frame-like light-shielding plate for supporting panel 1. Some of the beams of illumination light A from light source 2, which are incident on display portion (i.e., a display area) 1a of panel 1 pass through panel 1. However, the beams incident outside display portion 1a are shielded by panel 1 and light-shielding plate 7. Therefore, only the beams passing through display portion 1a of panel 1 are projected onto screen S.
The conventional liquid crystal projector enlarges and projects the image displayed on liquid crystal display panel 1 onto screen S. According to the liquid crystal projector, slide films need not be inserted or extracted, unlike in the conventional projector using slide films. In addition, the conventional liquid crystal projector can project an animation such as a television image onto the screen surface.
In the conventional liquid crystal projector described above, in order to perfectly project an image onto screen S, illumination light A must be incident on the entire surface of display portion 1a of liquid crystal display panel 1. The normal shape of display portion 1a of panel 1 is rectangular, while the shape of the cross section of light A from light source 2 is circular. If the beam spot of light A is small, the illumination beam is not incident on the corners of display portion 1a of panel 1, so that incomplete circular image is projected onto the surface of screen S.
In the conventional liquid crystal projector described above, the diameter of reflector 4 of light source 2 is selected to be large enough to cover the circumcircle of rectangular display portion 1a of panel 1, so that the entire display portion 1a of panel 1 can be illuminated. With the above arrangement, a perfect image without corner omissions can be projected onto screen S.
In the conventional liquid crystal projector, however, since circular illumination light A is directly incident from light source 2 onto liquid crystal display panel 1, the amount of unused light (i.e, light shielded by the portion outside display portion 1a and by light-shielding plate 7) illuminating the portion outside portion 1a of panel 1 is increased. Therefore, light A from light source 2 cannot be effectively utilized. As described above, since the cross section of light A emitted from light source 2 and reflected by reflector 4 is circular while the shape of display portion 1a of panel 1 is rectangular, the amount of unused light emitting the portion outside display portion 1a is increased at portions above and below display portion 1a if panel 1 is located such that the longitudinal direction of display portion 1a extends horizontally, as shown in FIG. 2. Most of the beams of illumination light A from light source 2 are wasted.